


Friends with Fins (and Tentacles Too)

by majesticduxk



Category: Supernatural
Genre: Emotions, Fluff, Humour, Lonely!Cas, M/M, Mer!AU, Mer!Dean, Mer!Sam, Romance, Sweet!Cas, Sweet!Dean, Tentacles, courting, courting gifts, octo!cas, pre slash, protective!Sam
Language: English
Status: Completed
Published: 2018-12-24
Updated: 2018-12-24
Packaged: 2019-09-26 06:52:34
Rating: Teen And Up Audiences
Warnings: No Archive Warnings Apply
Chapters: 1
Words: 3,972
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/17137055
Author URL: https://archiveofourown.org/users/majesticduxk/pseuds/majesticduxk
Summary: Dean has been the provider all his life. He’s looked after his little brother - and he’s done a damn good job of it! But now Sam is more than capable of looking after himself, and where does that leave Dean? One day, Dean finds himself swept out past the mer village, and past the hunting grounds, into a place that no mer ever goes. And maybe… just maybe there lies the answer.





	Friends with Fins (and Tentacles Too)

**Author's Note:**

  * For [lenisseok](https://archiveofourown.org/users/lenisseok/gifts).



> a/n: this is my christmas gift for [nyeh413peasants](https://archiveofourown.org/users/nyeh413peasants) as part of the spn_j2_xmas exchange. Nyeh413peasants said they liked au’s, and mentioned mer!au’s. I totally meant to write a smutty octo/mer/mer threesome, but apparently all I could write was fluffy pre-wincestiel friendship, so hopefully you enjoy this. 
> 
> a huge thank you to relucant for reading through and waving pompoms for me.

“It’s just so _stupid_.”

Dean _definitely_ wasn’t pouting as he grabbed onto a kelp frond and pulled himself into flowing leaves. And he definitely wasn’t hiding. He was just… taking a manly personal moment. Because it just wasn’t fair! 

Dean was the big brother. That meant he was the protector. The provider. That’s how it had always been. Ever since the elder Winchesters had been taken in a shark attack, Dean had stepped up. There hadn’t been anyone else - Sam had been barely more than a fry! - so Dean took responsibility for his little brother. 

And he never resented it, not even a little! Sammy was the most important thing in his life. And Dean was good at looking after him. It was just… 

“Why is he so much bigger than me?” 

Flipping his fins petulantly, Dean let go of the kelp and allowed the current take him away. Stupid Sam could catch dinner anyway. Stupid Sam with his stupid hair and his stupid arms and… It was a stupid thing to get fixated on. Dean recognised that. Mers came in all shapes and sizes. Sam’s shape was just one of the best.

Closing his eyes, Dean drifted in the current and allowed his thoughts to dwell on Sam. With his shapely, shiny fins. And burnished bronze tail. And those big, strong hands. He even thought about the way Sam’s hair waved in the gentle around their home eddies, and how it shone in the sun’s light when they went to the surface. 

Dean was flushed just thinking about it. Ah fuck. He wasn’t going to lie to himself. His brother was one fine fish, and of _course_ Dean appreciated his aesthetics. And Dean wasn’t the only one. He’d seen all the other pretty mers making eyes at his little brother. Sure some of them were bad (he was keeping both eyes on that Ruby, because Sam may be strong and pretty, but he was a sucker for a big sad eyes), but others were amongst their schools finest. Dean couldn’t begrudge them, after all, Sam deserved the best. 

And Dean? Well, Dean just wanted his brother to be happy. And try as he might, he just couldn’t imagine a future for Sam that included Dean. More than once he’d imagined Sam dumping his sorry tail when he found himself a mate.

Shivering miserably Dean wrapped his arms around himself. He had to stop these stupid thoughts. They were making him cold. Rubbing his arms, Dean suddenly stopped. He was fucking freezing, and he as pretty sure it wasn’t his thoughts making him cold.

Shit! When did the water get so cold? Looking around, Dean watched the seascape pass him by. He didn’t recognise a single thing. The water was not only colder, but it was darker too. And the kelp forests were taller. And the wrong colour. These were a murky green, rather than the emerald of his backyard. 

With a quick flick of his tail, Dean was propelled out of the current and towards the kelp. 

To his disappointment, it wasn’t much warmed out of the current. Despite the cold though, Dean was intrigued. He must have gone south, and he’d never been south. Why would he? From the time they hatched, merfolk were told about the monsters to the south. Not that Dean believed in monsters. He could believe there was scary shit though. Only a shell murderer would live in this cold dark place - not that they’d get the dive on Dean. He was a mer in his prime and could defend himself against almost anything! Still. It might be a good idea to head home again. Just to be on the safe side. The fact that his tail was if he didn’t get back before Sam noticed was beside the point. Dean couldn’t imagine anything scarier than a pissed off Sam! 

Still… since he was here it wouldn’t harm anything to have a little look around. Dean entered the murky depths of the kelp forest. 

It took all of 45 seconds for Dean to decide he’d had enough. Hopefully he’ll beat Sam home… shouldn’t be too hard. Sam had to fend off all those single mers. 

Not that he knew if they were single. Or begrudged Sam his pick… oh for fuck’s sake, why was he thinking about this again? With a disgruntled flick of his tail, Dean heads against the current. 

Except. 

Except something flashed in the corner of his eye. And he should keep swimming… should ignore anything tempting in this cold and dark place… but he’s Dean. And Dean may be many things, but able to resist the bling is not one of them. 

Dean flapped around until the shiny thing caught the light again. And oh. It was a stone. Just sitting there.

It was shiny. 

And pretty.

And just sitting there, sparkling in the sand and silt. 

Without conscious thought, Dean found himself heading towards the stone. Not that he was so enamoured with the pretty thing that he stopped being sensible. Oh no, he definitely stopped a full second at the edge of the sand and looked around. Nothing _seemed_ to be wrong… 

Swimming forward, Dean picked it up. It was magnificent. A deep blue and just so _mesmerising_.

Dean is still staring at the stone when a voice rumbled from the kelp, heralding a large shadow. 

“Welcome little mer. I see you like my courting gift’

Dean screamed and promptly passed out. 

~o~ 

Coming to, Dean snuggled into the soft thing beneath him. Even as he squirmed, getting more comfortable, he noticed the kelp felt different. Opening his eyes, he sees murky green. Murky green? He was… cold! He was cold and this was the cold water kelp. Dean had been heading back to his cave, where it was warm, so why was he… 

Fuck! The stone. A quick squeeze assured him he still had the stone, but where was he, and what was- 

“So you like my courting gift?” 

Dean screamed again. A large blob emerged from the shadows and Dean brandished the stone at his adversary. 

“Don’t take one step closer or I’ll… I’ll…” 

Dean’s hand dropped as he took in the creature in front of him. It was tentacled. And there were a lot of tentacles. Smooth, shiny tentacles that… that belonged to an evil creature. Snarling, Dean lifted his useless weapon once again, only to find himself face to face with the saddest eyes he’d ever seen. 

“You don’t like my gift?” 

Oh god. An octo. 

Dean had never met an octo, but he knew they were evil creatures intent only on death and destruction. They hid in the cold depths and only emerged to kill their prey. 

Except this one. He didn’t look like it was about to kill him. Cry on him, maybe.

“Are you going to kill me?” 

Dean winced. Perhaps his subtlety could use a little work. 

The octo managed to look even sadder, his tentacles, which had been a deep shiny black, faded to a grey-green colour, and curled in towards him. It wasn’t a great look. 

“I… no. No, I would never! I never meant to…” 

The words fade, and Dean watched as the octo twisted his hands together, glancing from Dean’s hands to his face. Dean followed his eyes, and remembered the stone in his hands. Holding it aloft, he laughed what he hoped was a natural laugh. 

“Not that I’d be able to do much with this. I guess if I threw it?” 

The stone was perfectly round. Actually, it was just perfect. Perfectly round. Perfectly coloured. It even fit perfectly in his hand. Hang on… what had the octo said?

“Do… do you not like my courting gift?” 

Riiiiiight. Courting gift. 

“Buddy, this ain’t no courting gift-” 

Fuck! The octo went grey and became smaller! What the fuck? Was it dying? Dean hadn’t even touched it? 

Without realising it, Dean had drifted forward, his hand now wrapped around the (soft and supple) tentacle of the octo. It felt surprisingly strong. Could probably hold him well. Maybe even rip him in half… Dean eyed the octo again. The spot where his hand touched was turning into a deep blue, but the rest of it was still that sickly grey. 

“You aren’t going to die are you?” 

The octo glared at him and Dean winced. Yeah, he definitely needed to work on his tact. Blushing slightly, Dean looked back at the stone. At the courting gift. And what even was his life? 

One of the other tentacles prodded him. “Do you like it?” 

“It’s gorgeous” Dean informed him. Because it was true. Dean loved it. “But normally…” he coughed uncomfortably. “Like… I’m a strong hunter. Normally I would do the courting…” 

Cas looked at him, his eyes brightening and his tentacle pulsing gently beneath Dean’s hand. “You… want to court me?” 

Dean flipped back. What? No! That… 

Well fuck. It wasn’t what he meant, but it sure as hell was what he said! 

“No! No, that’s not what I mean. I mean you’re not bad looking. If you weren’t an octo you might be a mermaids wet dream,” which ok, what the fuck did that even mean? Only octos had tentacles, and possibly only Dean dreamed about said tentacles, “but the thing is you generally only court people you know. Like, know very well. And we’re strangers! I don’t even know your name!”

“Castiel.” 

Dean wobbled his head. “What the fuck is a castiel?” 

The octo glared at him. “Me. I am a castiel. No! I _am_ Castiel.” When Dean continued to look blank the octo sighed at him. “My name is Castiel.”

Oh right. Dean felt stupid. “Casssstiel. Castielll. Castiel.” Dean tried it out a few times before shaking his head. “That’s a long fucking name. Cas'll do. Heya, Cas. I’m Dean.” 

The octo - Cas - seemed to puff up, his tentacles darkening to black again. 

“Hello, Dean. I am very pleased to meet you.” 

And weirdly, Dean believed him. They stared at each other, for how long Dean didn't know, before Castiel reached out a tentative tentacle. 

“So I just need to get to know you? I can do that! I can… if you will let me that is?” 

As Cas became more animated, his tentacles became a shiny blue. Quite like his eyes. (And quite like a certain shiny stone, that stupid part of Dean’s brain that liked tentacles informed him. Dean, of course ignored it). 

He couldn’t really ignore Cas’ hope though. God! He was like a kicked cuttlefish shown some love for the first time. Dean knew should turn him down now. He was a monster of the cold, and Dean was… Dean was lusting after his brother, and somehow found himself agreeing to accept Cas’ courtship. 

He even allowed Cas to carry him home. But only because he knew it would take him much longer to get there, and Sam would lose his fucking hair if Dean took much longer. 

He knew it was a bad decision, but couldn’t help smiling when he turned back and and saw Cas waving his arms and his tentacles hopefully.

~o~ 

“Where the fuck were you Dean?” 

Dean gasped and floundered as Sam slammed him into a wall. It was all dramatics though - Sam’s hands were gentle as they moved over him, making sure Dean was unharmed. Luckily there wasn’t a scratch on him but-

“What’s this?” 

\- he’d had no time to hide his stone. Not that he should have to. He was a… what would you even call him? A courtee? Was that even a thing?

“I said, Dean, what. Is. This.” 

Semantics, Dean told himself. Although he’d find out what his official title was as soon as Sam let him go. 

“Ah, this. This has a bit of a story to it, Sam-” 

Dean launched into a long and involved explanation about Cas and the courting stone. He was doing his best to paint Cas in the best possible light, but Sam got quieter and quieter. And that was never a good sign.

“I wasn’t pressured or anything!” Dean thinks about it. “Well… not really. But man, he looked like a kicked cuttlefish and I just couldn’t do anything but say yes. And it’s not like we’re engaged. It’s just a courtship, we’re just-” 

Sam didn’t even wait for Dean to finish the sentence before he swept out of the room. 

Then promptly swept back in again to grab Dean’s gift. 

“Hey wait! You can’t take that! It’s mine!” 

But Sam was long gone. 

~O~ 

Even the cold currents couldn’t cool him down. 

Sam swam angrily downstream until the kelp grew taller and darker and moved more sluggishly. he saw the kelp forests. Swimming out of the southern current, he started bellowing for Castiel. Who did this octo think he was, trying to steal his brother? Sam was ready to fight the monster. 

Out of the corner of his eye he saw a movement. Sam spun and watched as dark blue tentacles emerge from the shadow. he bellows for Castiel, ready to fight this monster for his brother. 

What he got was… quite unexpected. 

An octo - one that could only be Castiel, given the shiny blue of his limbs and eyes, drops down. Even as Sam pulled back a fist, ready to punch this monster right in the face, the octos face lit up, and he grabbed Sam’s hand. But he didn’t squeeze it and try to break his fingers, which is totally what Sam would have done. Instead he _shook_ it. What?  
“You must be Sam! Dean told me so much about you. He is very good at describing things. You do have beautiful long hair and a shiny bronze tail.”

The octo paused and looked at his own inky tentacles. He dropped Sam’s hand before easing back into the kelp, a sad look on his face. Sam groaned internally. He really did look like a kicked cuttlefish and everything in Sam just wanted to make him feel better. 

He had a soft spot for cuttlefish.

“Dean told me about you too.” Sam couldn’t help it if he sounded gruff and annoyed. He kinda was. This… this _stranger_ had no right to come and _court_ Dean! Dean was Sam’s! And obviously Dean didn’t quite recognise that, but after he’d dealt with the octo… 

“Castiel.” 

“What?” Sam flipped back at the octo’s voice. 

“My name is Castiel. Not… not _octo_.” The octo - _Cas_ \- floated there for a few moments wobbling his head. He obviously decided something, because he straightened his back and looked Sam in the eyes. 

“I like your brother.” 

Sam puffed up. He couldn’t help it. Because _he_ liked his brother. And no damn octo was going to steal him away. 

Castiel rolled his eyes. “Of course I won’t steal him away. Because Dean gets to _choose_.”

And now Sam was embarrassed. Not only was he speaking his thoughts out loud, but he was getting called out by an octopus. Great.

Cas scowled at him. 

“I know you are intelligent. At least, I know Dean _believes_ you are intelligent. Which means you are being deliberately obtuse.” Cas paused then, to glare at Sam before his expression softened. “I suppose that runs in the family. However - that is not what I mean. I mean it is, because Dean is his own mer and can make his own choices, and I would never even _dream_ of taking that away from him. Even if…” 

Cas trailed off, his face wavering. Sam had to laugh. He could tell what the Cas wanted to say. 

“Even if most of his decisions are ridiculous.” 

Cas’ face lit up as he smiled back. “He does appear to lack common sense. But, no that isn’t what I mean. Dean… Dean is going to be my friend! And even if he chooses not to accept my courting, I hope he will continue to be my friend. I don’t have many friends…” The last was said so quietly Sam was sure he was not meant to hear. “However! Dean values your opinion so… Sam?!” 

Sam’s life flashed before his eyes as he choked on the water. Even as he clutched at his throat his brain was in hysterics. Dean? Stubborn, fiery, always-knows-best Dean, valued his opinion? Oh god! These were his last moments? Thinking about the stubborn ass brother he’d never get to- 

His thoughts were momentarily derailed as Cas wrapped two firm (yet surprisingly soft) tentacles around Sam’s middle, while Cas’ balled fists settled at the base of Sam’s diaphragm. Sam fought against the hold, but then Cas shook him and pushed and - 

With a choked gasp Sam broke free. 

Spinning around, Sam clutched at his throat, and glared. 

“What the fuck were you doing! Trying to kill me? I knew you couldn’t trust an octo! I should have-” 

Sam’s diatribe abruptly halted as he noticed Cas melt back into the kelp. He’s turned a weird grey-green colour that matched the sluggishly moving fronds. It wasn’t a great colour on him. Lips forming a straight line, Sam took a deep a breath and attempted to centre himself. It was a great technique. One that usually had a great success rate. However, Sam managed to choke on the water yet again. As he clutched at his throat, he couldn’t help notice the way Cas darted forward before swaying uncertainly at in the kelp. 

He was only trying to help. And more than that, he _had_ helped. He’d actually saved Sam’s life. Dammit! Sighing, Sam wiped a hand over his eyes. 

“Gotta be honest with you, Cas.” And good grief, the words had Cas’ limbs dotted with colour. And excited red dotted the bleak grey-green. Idly Sam wondered if the colours meant anything. Regardless, Sam could feel the waves of terror and excitement coming off Cas. Sam had to put an end to it. “Yes. Gotta be honest. I haven’t heard anything good about octos-”

And yes. Sam was the asshole responsible for the way Cas drooped, his tentacles turning an even more unhappy grey. Fuck.

“- but you seem great.” 

It seemed to take a few moments before the words to filter through. And while Cas’ face remained stoic his eyes were hopeful. And his tentacles were were getting little yellow splotches on them. 

“I do?” 

Yep. Cas could hide behind his voice, but those tentacles were wiggling with excitement. Sam tore his eyes away. 

“You do. And I’m being an asshole. For many reasons. Because I’ve heard the rumours about this part of the ocean-”

“You’ve never been here!” 

“Because I’m embarrassed I choked on water-” 

“That really was ridiculous.” 

“- _and_ ,” Sam continued forcefully, “because Dean came back with a fucking _courting_ gift-” 

Cas didn’t interrupt, but he did look smug. 

“Yeah, yeah, _your_ courting gift.” 

Sam swam towards Cas, and settled himself in the kelp beside him. 

“I’m sorry, Cas. I came here all guns blazing and it wasn’t fair to you. You’re a good guy. And I want to give you a chance.” 

Cas looked at him, thoughtful. 

“A chance to what?” 

Sam shrugged. “I don’t know. I really don’t know. When Dean got back he was all full _I met this awesome dude in the kelp forests_ and then he showed me the gift and I just saw red. He’s never spoken like that before.”

“What did he say?” 

Sam was not immune to Cas’ hopefulness. 

“He said you had gorgeous dark tentacles-” the excited red spots had faded, but at Sam’s words they flushed to pink. “And he mentioned the shiny blue, but they haven’t looked dark and glossy to me.” 

There was a question there, and Cas coughed uncomfortably. 

“Uh, you seem to have noticed that my tentacles are…” Cas waved an embarrassed peach on around and Sam smirked. “Well… uh, glossy dark is…” 

And now Cas’ face was as flushed as his tentacles. Sam frowned a moment before his eyes bulged. “You were _horny_?”

“Sam!” Cas hissed at him. “I… Dean is very comely, and he’d been rolling around and moaning in my bed and…” Cas hissed again. “I don’t want to talk about this.” 

Sam laughed at him, as Cas resettled himself and harrumphed grumpily. “Anyway, after Dean’s visit I took him home, and he talked about you all the way there. I heard to much about his amazing brother - which is you, Sam.” 

Sam rolled his eyes and hid a grin. Cas sounded very serious. 

“And your tail and your hair and your adventures.” Cas sighed. “So of course I wanted to meet you! I… I don’t have many friends here. Octofolk are rather solitary, except for when we take a mate, but I always wanted friends. But not many others really like octos…” 

Cas stirred the sand at their feet with a sad, solitary tentacle and Sam’s heart melted. Stupid cuttlefish octo. He placed one gentle hand on Cas’ tentacle, waiting until he looked up. 

“I’m willing to change my mind.” 

~O~ 

If anyone asked, Dean had been busy doing something important stuff. Really important do not disturb stuff. In actual fact, he’d swum around in circles, wondering if he should chase after Sam and save Cas.

Sure, Cas was a scary dude with 8 tentacles and two well chiseled arms, but Sam was an even scarier dude with two even more well chiseled arms. No tentacles, but that probably wouldn’t stop him. 

And Cas wasn’t even though tough! He was just a cute little cuttlefish that needed rescuing, and Dean was just mer to do it!

Decision made, Dean flung himself out the door, and straight into the arms of a smug looking Sam. Before Dean could pull himself free, Sam had somehow managed to wrap his arms around him and dip him (and what the hell? Who does Sam think he is? Arial?). Growling, Dean attempted to pull out of his brothers arm, but the bull shark dragged him back into their cave. 

“Sammy! Put me down! I have to go rescue Cas!” 

Sam leisurely swam to the bed, before placing Dean gently down. Sam smiled at him softly.

“You look all excited.” 

Dean batted at his hands. “Fuck that. I have to help Cas!” 

Sam’s soft smile slipped, and he frowned at Dean. “

“Help Cas? Why? What happened to him? He was fine when I left him.”

t was Dean’s turn to frown. “He was what?” 

“Fine.” 

Dean shook his head, then twisted a finger in both his ears. “Sorry, Sam. I thought I heard you say he was _fine_ , which makes no sense, as you definitely weren’t heading out for a chat before.” 

Sam’s expression morphed into a combination of pleased and embarrassed. 

“I may have been too hasty, Dean. Cas… Cas seems like a good guy. And he maybe might... ” 

Dean just crossed his arms and stared at his brother. When there was no response he raised a brow as well. “He maybe might what?” 

Spinning on his tail, Sam threw something on Dean’s bed. “He maybe might have sexy tentacles, and I maybe might have told him I liked them.” 

To say Dean was flabbergasted was an understated. 

“You _what_?” 

That wasn’t fair! Dean was the one who liked tentacles, and even _he_ had enough fucking decorum to not rub himself all over them. And Dean had a better reason that Sam! At least Dean had been kidnapped. All Sam did was go to start a fight. No fucking fair! What was he doing checking out Cas’ tentacles? Actually now that he actually looked…

“Sam. Why are there _two_ shiny blue stones on this bed?” 

Sam just floated there looking smug. 

Well not for long, Dean decided. His brother had a hell of a lot of explaining to do!

**Author's Note:**

> Hey it's christmas day here - happy christmas! This was fun to write and I hope it's fun to read. I almost wrote fin to read, which would have been correct too xD leave me a note letting me know what you think!


End file.
